1. Field of the Invention
The present invention relates to an electron-beam exposure system and an electron-beam exposure method. Specifically, the present invention relates to a multicolumn electron-beam exposure system in which a plurality of columns are arranged above a single wafer, and which performs exposure processes in the columns simultaneously, and relates to an electron-beam exposure method using the exposure system.
2. Description of the Prior Art
In a case of conventional electron-beam exposure systems, a variable rectangular opening or a plurality of stencil mask patterns are prepared in a stencil mask. One of the mask patterns is selected by means of beam deflection, and the mask pattern thus selected is transferred onto a wafer by exposure. In the case of these electron-beam exposure systems, a plurality of mask patterns are prepared. However, it is one electron beam that is used for the exposure, and thus, it is only one mask pattern that is transferred thereon at a time. For this reason, in order to make a workpiece full of formed patterns, the patterns are formed in a way that the patterns are arranged next to one another.
As one of such electron-beam exposure systems, an electron-beam exposure system which performs a “partial one-shot exposure” has been disclosed, for example, in Japanese Patent Laid-open Official Gazette No. 2004-88071. What the “partial one-shot exposure” means is as follows. To begin with, by means of beam deflection, one pattern area is selected out of a plurality of stencil patterns, for example, out of one hundred stencil patterns, which are arranged on a mask. Then, a beam is irradiated on the pattern area thus selected, for example, in a 300 μm×300 μm area. Thereby, the cross section of the beam is shaped into a form identical to the selected stencil pattern. Subsequently, the beam, which has passed through the mask, is swung back by a deflector in the subsequent step. Then, the cross section of the beam is reduced with a certain reduction ratio, for example, 1/60, which is determined by the electro-optic system. Thus, the selected stencil pattern is transferred onto the workpiece. An area of the workpiece on which the beam is irradiated at a time is, for example, 5 μm×5 μm in size. If a stencil pattern on the mask is adequately prepared corresponding to a device pattern to be obtained by exposure, this makes it possible to reduce the number of necessary exposure shots to a large extent, and to increase the throughput, in comparison with a case where only a variable rectangular opening is used.
In addition, a multicolumn electron-beam exposure system has been proposed (see Haraguchi, T., et. al., J. Vac. Sci. Technol, B22(2004)985). The multicolumn electron-beam has a configuration in which a plurality of such columns in a reduced size (hereinafter referred to as “column cells”) are arranged collectively above a wafer, and performs exposure processes in the plurality of column cells simultaneously. Each of the column cells is similar to the column of the single-column electron-beam exposure system. However, the multicolumn electron-beam exposure system performs the processes in parallel. Accordingly, this makes it possible to increase the throughput of exposure by K times (K=the number of columns).
As described above, a multicolumn electron-beam exposure system which performs parallel processes by use of a plurality of column cells for the purpose of increase the throughput of exposure has been proposed. In order to increase the throughput of exposure by use of a multicolumn electron-beam exposure system of this type, the column cells need to be designed to have the same functions to the respective beams passing through the column cells.
Each column cell has an individual mechanical error in association with the manufacture and an individual assembly error. As a result, slight difference in lens intensity and deflection efficiency concerning a beam occurs among the column cells, even though the same lens conditions and deflection data are given to the column cells. For this reason, individual lens power supplies and individual control systems are prepared respectively for the column cells. Thus, outputs from the lens power supplies and control outputs from the control systems are determined in order that beam characteristics respectively of the column cells become the same. The individual lens power supply independently drives the lens in each of the column cell. The control system controls deflection efficiencies of the deflectors and outputs from the compensation coils in each of the column cells.
Specifically, a current value of the workpiece, beam deflection positions, in-shot intensity distributions and the like are measured by use of an ammeter, back-scattered electron detectors and secondary electron detectors. On the basis of the result of the measurement, the outputs from the lens power supplies and the control outputs from the control systems are determined in order that the beam characteristics of all of the column cells become identical to one another.
In some cases, however, it is difficult to measure the beam characteristics by use of the aforementioned method. For example, with regard to a characteristic of a variable-shaped beam whose cross-section has a rectangular shape, the more microscopic the beam is, the smaller the beam current is. Accordingly, it is difficult to precisely measure the current value of the workpiece, the beam deflection positions and the in-shot intensity distributions. For this reason, in a beam adjusting step of determining a value of the output from the lens power supply and a value of the control output in each of the column cells, the value of the output from the lens power supply and the value of the control output are determined on the basis of a beam whose cross section is a variable rectangle, but which is not reduced to be microscopic. This case causes a phenomenon where a pattern obtained by exposure using a variable-shaped beam whose cross section has been shaped into a microscopic variable rectangle is different from a desired pattern.
As a countermeasure against this, it is conceivable that the exposure data themselves are corrected in order that the size of a pattern to be actually obtained by exposure can correspond to an intended size. However, this is not an effective method for the multicolumn electron-beam exposure system. Specifically, if exposure data themselves are intended to be changed with regard to patterns to be exposed respectively in the column cells in order that the sizes as the result of the exposure become the intended sizes, this change requires the exposure data to be prepared for every column. Accordingly, this is unrealistic in view of data capacity and time that are required to establish the corrected data.